1. Field of the Invention
This invention relates to solid state devices and, more particularly, to solid state display devices.
2. Art Background
Electrochromic devices potentially offer certain significant advantages, e.g., memory. These devices are generally composed of (1) a liquid electrolyte, (2) an electrode which changes color upon application of an appropriate voltage to the device, i.e., an electrochromic electrode, and (3) a counterelectrode to this electrochromic electrode. For example, cells based on a liquid electrolyte using either an anodic iridium oxide (see, for example, S. Gottesfeld et al, Applied Physics Letters, 33, 208 (1978) and G. Beni and J. Shay, Applied Physics Letters, 33, 567, (1978)) or a tungsten bronze, M.sub.x WO.sub.3, electrochromic electrode (see Faughnan et al, RCA Review, 36, 177 (1975) and M. Green et al, Thin Solid Film, 38, 89 (1976)) have been reported. A very limited number of electrochromic cells based on all solid state components have been disclosed. The most widely studied of these cells utilizes a Na.sub.x WO.sub.3 electrode with a solid Na-.beta.-Al.sub.2 O.sub.3 electrolyte. Both liquid and solid configurations have their respective advantages. However, the potential for application of fabrication technology developed in conjunction with transistor devices is an alluring attribute of solid state electrochromic devices.
Despite the enticement of a developed fabrication technology, it is quite difficult to produce practical solid-state electrochromic display devices. Different electrochromic devices depend on different mechanisms for producing the electrochromic effect. Different mechanisms usually require different type materials which, in turn, lend themselves to different fabrication techniques. Even when considering a single electrochromic material, different techniques have led to widely divergent results. Thus, the development of solid state electrochromic devices, despite the advantages possibly afforded, has not been extensively exploited.